The 'Slipper animalcule' is:

The cell wall of diatoms is composed of .........

All protozoans have

Which group of protozoans consists entirely of parasites?

The given statements are some characters of a particular group of Kingdom $Protista$.
$(i)$ Most of them are freshwater organisms found in standing water.
$(ii)$ They have a protein-rich layer (called pellicle) which makes their body flexible.
$(iii)$ They have two flagella,a short and a long one.
$(iv)$ Though they are photosynthetic in the presence of sunlight,but in the absence of sunlight they behave like heterotrophs by predating on other smaller organisms.
Identify the correct group on the basis of these characters.

Which of the following algae secretes 'saxitoxin'?